The present invention relates to a manifold gasket with a deformation absorbing mechanism, which can securely seal around manifold holes without being substantially affected by expansion and retraction of the manifold by heat.
A manifold attached to an internal combustion engine is exposed to high temperature by exhaust gas when the engine is actuated, while the manifold is cooled to an ambient temperature when the engine is stopped. Namely, the manifold is expanded and contracted cyclically by heat of the engine whenever the engine is operated and stopped. Thus, it is not easy to securely seal around the manifold holes by a manifold gasket. Also, in case sealing portions for the adjacent holes of the manifold gasket are connected together to form one manifold gasket, the manifold gasket may deform by heat to cause a sealing problem.
A conventional manifold M and a gasket G for use in a four cylinder engine are shown in FIGS. 1 and 2. The manifold M is formed of a main portion 10 and four branched portions 11. Inlet portions 12 of the branched portions 11 are attached to outlet ports or portions 13 of an engine 14, and are connected together by bolts 15.
The branched portions 11 of the manifold M are united together at the inlet portions 12 by flanges 16 to facilitate attaching operation of the manifold M to the engine 14. Also, the gasket G includes sealing portions 17 attached to the inlet portions 12, which are connected together by flanges 18. The shapes of the sealing portions 17 and the flanges 18 of the gasket G substantially correspond to those of the inlet portion 12 and the flange 16 of the manifold M.
When the engine 14 with the manifold M and the gasket G is actuated, the manifold M is heated to high temperature by exhaust gas, while the engine 14 is not so heated due to a cooling system of the engine. Thus, the flanges 16 of the manifold M expand in the longitudinal direction, as shown in arrows 19, and the center area of the manifold M is pushed toward the engine 14, as shown in an arrow 20. Therefore, the gasket G suffers damage at the sealing surfaces due to the movement between the inlet portions 12 and the outlet portions 13 whenever the engine is operated and stopped, so that the sealing ability of the gasket G decreases.
In order to resolve the problems of the conventional gasket, a gasket G' as shown in FIG. 3 was proposed in Japanese Utility Model Publication (KOKAI) No. 59-110471. The gasket G' is formed of an upper plate 21 with spacers 22 at longitudinal ends, a middle plate 23 with beads 24, 24' for sealing around the manifold holes, and a lower plate 25 situated under the middle plate 23.
When the gasket G' is installed, the beads 24 are compressed strongly by the spacers 22, but the beads 24' are only slightly compressed. When the center area of the manifold M is pushed toward the engine due to heat as explained before, the beads 24' can be compressed to absorb the deformation of the manifold M. Thus, damages and decrease of the sealing ability of the gasket G' are prevented.
However, in the above gasket G', since the beads 24 are always compressed strongly by the spacers 22, the beads 24 receive surface pressure stronger than that at the beads 24'. Thus, the beads 24 suffer deformation by heat, so that the beads 24 may not properly seal for a long usage.
On the other hand, in order to adjust a surface pressure of a bead, an auxiliary plate may be installed on a plate with the bead, for example as disclosed in U.S. Pat. No. 4,728,110. Namely, the auxiliary plate is located adjacent to the bead so that the bead is not fully compressed and the compression force to the bead is applied to the auxiliary plate.
However, there is no manifold gasket for properly sealing around the manifold holes while preventing creep relaxation of the beads and absorbing deformation of the manifold.
The present invention has been made in view of the above drawbacks, and an object of the invention is to provide a manifold gasket with a good sealing ability for a long usage.
Another object of the invention is to provide a manifold gasket as stated above, which can properly absorb deformation of manifold flanges of a manifold though the manifold flanges attached to the manifold are deformed due to heat in operating an engine.
A further object of the invention is to provide a manifold gasket as stated above, which can be manufactured easily and economically.
Further objects and advantages of the invention are apparent from the following description of the invention.